Getting ready to mount a 2m Yagi on a Az/El rotator on top of the school for an upcoming ARISS contact. My question is, how high above the roof should I mount the antenna system? Or more clearly, when the antenna is positioned 90 degrees in the vertical, how much clearance should there be between the back end of the antenna and the roof? Your thoughts please.

A half wavelength would be the number I'd pick, to help preserve the pattern of the beam in the proximity to other objects.

Most important is the view to the horizon, to maximize the time you have for the pass. I would pick the antenna location that offers you the least obstructed view of the track over most anything else. The ISS is very strong compared to the FM LEO's so once you have it in view, you shouldn't have any issues with signal strength even with a modest antenna.

I was thinking a full wavelength. Things are pretty flat here in Houston. From the top of the school building which is about 30 feet up we have an unobstructed 360 degree view of the horizon. I guess it isn't totally unobstructed as we are looking over housing developments, but pretty much so. No big buildings, water towers, or mountains in the way. So the view is pretty good. We have a mast mounted on the side of the building that rises about 5.5 feet above the roof line. The M2 Yagis we are using extend about 54 inches behind the cross boom on the rotator. In the vertical position bottom of the antenna will be about a foot above the roof. I guess I need to see if I can get the mast pushed up about 3 or 4 feet.

Yep it is a big commitment, but it will be worth it. The bottom line is that we are asking to play in a limited game, and if we want to play in the game we have to follow the rules. I personally feel the requirements are a bit overkill, but from a NASA PR perspective, they want to make sure it is a success. I understand that. It is a major year long+ project for our school, so we want to make sure it is a success as well.

I am having a lot of fun with the project and I know the students are going to be very proud when we pull it off. It will be a major shot in the arm and a source of pride for our low performing school. It will be a great PR event for our district as well.

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